U.S. patent number 6,148,923 [Application Number 09/219,054] was granted by the patent office on 2000-11-21 for auto-cycling plunger and method for auto-cycling plunger lift.
Invention is credited to Dan Casey.
United States Patent |
6,148,923 |
Casey |
November 21, 2000 |
Auto-cycling plunger and method for auto-cycling plunger lift
Abstract
An auto-cycling plunger and method for lifting out condensate
and fluid that accumulate and retard production in oil and gas
wells. The auto-cycling plunger comprises a tube that defines an
inner chamber, one or more flapper sealing rings mounted on the
tube and a detachable valve member positioned at one end of the
tube. During the method, the auto-cycling plunger free falls down
the production tubing string with the detachable valve accelerating
faster than the tube. The detachable valve hits the bottom-hole
spring first, the tube follows and engages with the detachable
valve thereby creating a seal. The liquid collects above
auto-cycling plunger and the plunger moves up the production tubing
as gas within the well accumulates below it and creates an upward
pressure. The auto-cycling plunger repeats it's movement up and
down the well without having to shut-in the well thereby
continuously removing liquids without stopping production.
Inventors: |
Casey; Dan (Huntsville,
TX) |
Family
ID: |
22817658 |
Appl.
No.: |
09/219,054 |
Filed: |
December 23, 1998 |
Current U.S.
Class: |
166/372; 166/329;
166/53; 166/68; 417/552; 417/555.2; 417/56 |
Current CPC
Class: |
E21B
43/121 (20130101) |
Current International
Class: |
E21B
43/12 (20060101); E21B 043/00 () |
Field of
Search: |
;166/53,372,68,105,70,153,156,329,105.5
;417/555.2,555.1,554,56,60,552 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Batson; Victor
Attorney, Agent or Firm: D'Ambrosio; Jo Katherine
Claims
What is claimed is:
1. An auto-cycling plunger for lift of condensate and fluid out of
a gas or oil well, the plunger comprising:
a tube having an upper section, a middle section, and a lower
section, the lower section forming a retrieval end, the upper
section, middle section and lower section defining a continuous
chamber;
one or more flapper sealing rings mounted along the tube, the
sealing rings extending outwardly from the tube; and
a detachable valve member positioned at the retrieval end.
2. The auto-cycling plunger of claim 1 wherein the upper section
comprises an internal wall and an external wall, the internal wall
defining one or more grooves.
3. The auto-cycling plunger of claim 1 wherein the middle section
of the tube comprises a central mandrel separate from the upper
section and the lower section, the central mandrel comprising an
upper end and a lower end for detachable engagement with the upper
section and lower section of the plunger.
4. The auto-cycling plunger of claim 3 further comprising at least
two spacers encircling the central mandrel.
5. The auto-cycling plunger of claim 4 wherein the one or more
flapper sealing rings are interposed between the spacers.
6. The auto-cycling plunger of claim 4 wherein the upper end and
the lower end of the central mandrel are threaded for detachable
engagement with the upper section and lower section of the plunger
so that the flapper sealing rings are held in place between the
spacers when the upper section is threaded onto the upper end of
the central mandrel and the lower section is threaded onto the
lower end of the central mandrel.
7. The auto-cycling plunger of claim 1 wherein the middle section
has an external wall and an internal wall and the flapper sealing
rings are mounted on the external wall so that the flapper sealing
rings extend outwardly from the plunger.
8. The auto-cycling plunger of claim 1 wherein the flapper sealing
rings are flimsy, elastomeric sealing rings.
9. The auto-cycling plunger of claim 8 wherein the flapper sealing
rings are sized to cause a positive seal when placed within a
production string tubing of the gas well.
10. The auto-cycling plunger of claim 8 wherein the outer diameter
of the flapper sealing ring has an interference fit with production
string tubing of the gas well.
11. The auto-cycling plunger of claim 8 wherein the outer diameter
of the flapper sealing ring is between about 2% to about 8% larger
than the inner diameter of production string tubing of the gas
well.
12. The auto-cycling plunger of claim 1 wherein each of the flapper
sealing rings comprises a width to thickness ratio within a range
of from about 0.1 to about 0.2.
13. The auto-cycling plunger of claim 1 wherein the retrieval end
of the lower section is angular-shaped to align and receive the
detachable valve member.
14. The auto-cycling plunger of claim 1 wherein the retrieval end
of the lower section comprises a scraper edge for paraffin removal
from inner walls of production string tubing.
15. The auto-cycling plunger of claim 1 wherein the detachable
valve member comprises a sphere sized to be received within the
retrieval end of the plunger.
16. The auto-cycling plunger of claim 15 wherein an inner diameter
of the retrieval end is within a range of from about 1/4 mm to
about 3 mm larger than the diameter of the sphere.
17. The auto-cycling plunger of claim 1 wherein the detachable
valve member comprises a bullet-shaped shuttle having a spherical
end, the spherical end sized to be received within the retrieval
end of the plunger.
18. The auto-cycling plunger of claim 17 wherein an inner diameter
of the retrieval end is within a range of from about 1/4 mm to
about 3 mm larger than the diameter of the spherical end of the
bullet-shaped shuttle.
19. The auto-cycling plunger of claim 1 wherein the retrieval end
of the lower section comprises an inner wall and an outer wall, the
inner wall defining at least one groove for receiving an O-ring,
the O-ring sized so that it fits snugly about the detachable valve
member when the detachable valve member is engaged within the
retrieval end of the plunger.
20. The auto-cycling plunger of claim 19 wherein the inner wall of
the retrieval end forms a seat for sealing the lower section when
the detachable valve is engaged within the retrieval end.
21. The auto-cycling plunger of claim 19 wherein the inner wall of
the retrieval end forms a sealing groove and an O-ring is fitted
within the sealing groove for sealing the lower section when the
detachable valve is engaged within the retrieval end.
22. The auto-cycling plunger of claim 1 wherein the retrieval end
further comprises a choke.
23. The auto-cycling plunger of claim 1 wherein the upper section,
middle section and lower section form an integral tube having an
inner wall and an outer wall, and the flapper seals are mounted on
the outer wall of the tube so that they extend outward from the
tube.
24. The auto-cycling plunger of claim 1 wherein the upper section
and middle section form an integral tube having an inner wall and
an outer wall, the tube further comprising the flapper seals
mounted on the outer wall of the tube so that the seals extend
outward from the tube.
25. A method for auto-cycling plunger lift in a gas or oil well
having a lubricator positioned at a top of a production string
tubing and a bottom-hole bumper spring positioned at a bottom of
the production string, the lubricator comprising an arrival spring
and a catcher, the method comprising:
a) stopping production flow;
b) placing auto-cycling plunger with a detachable valve member in
the lubricator so that they are held by the catcher, the
auto-cycling plunger comprising a retrieval end and flapper sealing
rings;
c) starting production flow so that said gas well is
pressurized;
d) releasing the catcher thereby allowing the detachable valve
member and auto-cycling plunger to fall independently through the
production string tubing until liquid in the bottom of the well
collects at top of said plunger;
e) striking the bottom-hole bumper spring with the detachable valve
member;
f) striking the bottom-hole bumper spring with the plunger so that
the retrieval end of the plunger captures the detachable valve
member causing a valve seal within the plunger as formation gas
pressure pushes against the detachable valve member;
g) effecting a seal between the flapper sealing rings and the walls
of the production string tubing;
h) allowing formation gas pressure to push the plunger with the
captured detachable valve member upward thereby pushing liquid
above the plunger towards top of the production string tubing;
i) drawing off liquid and piping out gas as the plunger reenters
lubricator thereby reducing pressure below the plunger;
j) allowing the detachable valve member and the plunger to fall
back down the production string tubing;
k) repeating steps e) through j) without shutting in well.
26. The method of claim 25 wherein the retrieval end of a lower
section comprises an inner wall and an outer wall, the inner wall
defining at least one groove for receiving an O-ring, the O-ring
sized so that it fits snugly about the detachable valve member when
the detachable valve member is engaged within the retrieval end of
the plunger.
27. The method of claim 25 wherein the inner wall of the retrieval
end forms a sealing groove and an O-ring is fitted within the
sealing groove for sealing a lower section when the detachable
valve is engaged within the retrieval end.
Description
FIELD OF THE INVENTION
The present invention relates to an auto-cycling plunger and method
for auto-cycling plunger lift of liquids during the production
phase of gas, oil or other types of wells, more particularly low
volume wells.
BACKGROUND OF THE INVENTION
Plunger Lift is the removal of fluid from the well formation using
the formation gas as the motive source. All natural gas wells
produce liquids with the gas flow. A problem arises when fluids
accumulate in the well bore of a gas well. This fluid can be fresh
water, salt water, condensate and/or oil that migrates toward the
well bore with the gas movement. Oil and condensate have market
value. In formations that produce unprofitable water, removal is
desirable because the presence of water retards and stops the
migration of gas to the well bore.
Newer, fast flowing wells atomize and blow this liquid to the
surface. Older wells have (or develop) a lower gas to liquid ratio
(GLR) that will not push all of the liquid up and out. In these
wells, the fluid falls back down the tubing string, restricting the
free flow of gas from the formation. A tall column of liquid in the
tubing can completely and effectively stop the flowing gas well.
Many wells had to be abandoned leaving significant amounts of oil
and gas within the well because the flow rate had decreased or
stopped completely.
The plunger was first employed for fluid removal about fifty years
ago. The first plungers were solid rods with concentric grooves
spaced along their outer surfaces. These grooves cause turbulence
as gas blows past the plunger. Gas escapes past the plunger due to
the absence of a sealing means. Turbulence produces drag which is
an aid in lifting the plunger. This style is called a spiral
plunger. There is of necessity an annulus between the spiral
plunger and the inner wall of the tubing string. Gas can leak
upwardly through this annulus.
More recently, U.S. Pat. No. 4,986,727 to Blanton discloses a
pressure-operated oil and gas well swabbing device. The '727
reference claims a pressure activated valve comprising a pressure
collapsible bladder means, a valve and seat interposed within the
fluid passage and means connecting the valve and seat to the
pressure collapsible bladder so that the valve and seat are closed
when the bladder is collapsed to a degree corresponding to
predetermined valve closing pressure. Fineberg in U.S. Pat. No.
4,984,969 teaches a plunger lift tool having a nose assembly to
slow the descent of the tool into the well, a valve assembly, and a
piston cylinder assembly. When the '969 tool is dropped, the gas
and liquids in the well flow through restrictions in the nose
assembly, thereby breaking the fall.
A pad plunger as disclosed in U.S. Pat. No. 4,531,891 improves the
sealing efficiency relative to the efficiency of the
above-described spiral plunger. The pad plunger comprises a central
mandrel encircled by articulating segmented pads. The pad shapes
vary from manufacturer to manufacturer. Four pads are the optimum
number for segmented sealing. Between the mandrel and each pad is a
suitable spring that pushes the pad outwardly for sealing contact
with the well tubing wall. However, gas pressure still escapes
between the pads and through the gaps in the various segments.
U.S. Pat. No. 4,984,970 to Flickman teaches an arrangement of coned
disc for a valve pumping chamber. These arrangements are used in
high pressure pumps. In the coned ring, a radial distance between
the ends of the seal portions is provided to secure that the ring
portion remains pressed against an adjacent portion when equal
pressures appear on both axial ends of the coned portion. The coned
ring is used in a pump to separate two different fluids from each
other.
A valveless plunger system for well pumping is disclosed in Martin,
U.S. Pat. No. 4,502,843. The groove and flange structure is used
for gas pressure lift. The valveless plunger begins descent when
the motor valve is closed. The plunger falls slowly under the
influence of gravity. A timer opens the motor valve to enable gas
to escape through a flow line. This creates a pressure differential
across the plunger and drives the plunger upward.
The extant plungers do work in removing liquids from wells that can
produce at least 300 cubic feet of gas for every barrel of fluid to
be lifted 1000 feet. The problem of routinely removing fluid from
oil and gas wells that have a G/L ratio below 300 cubic foot per
barrel of fluid lifted 1000 feet remains.
One aspect of the problem to be solved is inefficiencies in the
sealing means that is used to isolate the formation fluid from the
formation gas as the plunger travels up the tubing/casing string.
The typical plunger, moving upward, has fluid above it and gas
below it. The plunger is a traveling interface between the gas and
the fluid in the well tubing. Poor sealing causes the escape of gas
past the plunger and consequently, a loss of gas pressure required
for upward travel. Too tight a seal prevent rapid mobility and
problems with the plunger becoming stuck within the well tubing.
Another aspect of the problem is prior art plungers require that a
well be shut in during the use of the plunger lift tool.
None of the references teach or suggest an auto-cycling plunger nor
a method for auto-cycling plunger lift.
Consequently, there remains the need for an inexpensive and
effective tool and simple method for rapidly and repeatedly
removing liquids from low GLR wells. The problem of removing
liquids without shutting in the well must also be addressed.
SUMMARY OF THE INVENTION
The auto-cycling plunger and method for auto-cycling plunger lift
of the present invention allows low gas to liquid ratio wells to be
productive by effectively removing fluids that retards production.
Alternatively the plunger is useful in an oil well to promote the
movement of oil in low pressure wells up through the casing. The
improved seal between the production tubing and the plunger allows
a minimum of gas pressure to remove the liquid. The auto-cycling
plunger used according to the method of this invention permits the
removal of liquid from the formation without shutting in the well.
Another feature of the auto-cycling plunger is the ability to
remove paraffin buildup from the tubing wall as it is performing
and without shutting-in the well.
A preferred auto-cycling plunger for lift of condensate and fluid
out of an oil or gas well comprises a tube having an upper section,
a middle section, and a lower section, the lower section forming a
retrieval end, the upper section, middle section and lower section
defining a continuous chamber. Preferably, one or more flapper
sealing rings are mounted along the tube, the sealing rings
extending outwardly from the tube; and a detachable valve member is
positioned at the retrieval end. In one embodiment, the upper
section comprises an internal wall and an external wall, the
internal wall defining one or more grooves. the middle section of
the tube comprises a central mandrel separate from the upper
section and the lower section, the central mandrel comprising an
upper end and a lower end for detachable engagement with the upper
section and lower section of the plunger. A preferred auto-cycling
plunger further comprises at least two or more spacers encircling
the central mandrel. one or more flapper sealing rings are
interposed between the spacers.
Preferably, the upper end and the lower end of the central mandrel
are threaded for detachable engagement with the upper section and
lower section of the plunger so that the flapper sealing rings are
held in place between the spacers when the upper section is
threaded onto the upper end of the central mandrel and the lower
section is threaded onto the lower end of the central mandrel.
In one aspect, the middle section has an external wall and an
internal wall and the flapper sealing rings are mounted on the
external wall so that the flapper sealing rings extend outwardly
from the plunger. Preferably, the flapper sealing rings are flimsy,
elastomeric sealing rings and the flapper sealing rings are sized
to cause a positive seal when placed within production string
tubing of the gas well.
Preferably, the outer diameter of the flapper sealing ring has an
interference fit with production string tubing of the gas well; In
one aspect, the outer diameter of the flapper sealing ring is
between about 2% to about 8% larger than the inner diameter of
production string tubing of the gas well. In another aspect, the
flapper seal comprises a width to thickness ratio within a range of
from about 0.10 to about 0.20.
Preferably, the retrieval end of the lower section is
angular-shaped to align and receive the detachable valve member. In
one preferred embodiment, the retrieval end of the lower section
comprises a scraper edge for paraffin removal from inner walls of
production string tubing.
The detachable valve member can comprise a sphere sized to be
received within the retrieval end of the plunger. In this
embodiment, the inner diameter of the retrieval end is within a
range of from about 1/4 mm to about 3 mm larger than the diameter
of the sphere. Alternatively, the detachable valve member can
comprise a bullet-shaped shuttle having a spherical end, the
spherical end is preferably sized to be received within the
retrieval end of the plunger. In this embodiment, the inner
diameter of the retrieval end is within a range of from about 1/4
mm to about 3 mm larger than the diameter of the spherical end of
the bullet-shaped shuttle.
In another aspect of this invention, the retrieval end of the lower
section comprises an inner wall and an outer wall, the inner wall
defines at least one groove for receiving an O-ring and the O-ring
is sized so that it fits snugly about the detachable valve member
when the detachable valve member is engaged within the retrieval
end of the plunger. Preferably, the inner wall of the retrieval end
forms a seat for sealing the lower section when the detachable
valve is engaged within the retrieval end. The inner wall of the
retrieval end can form a sealing groove and an O-ring is fitted
within the sealing groove for sealing the lower section when the
detachable valve is engaged within the retrieval end. In one
embodiment, the retrieval end further comprises a choke.
In an alternative embodiment, the upper section, middle section and
lower section form an integral tube having an inner wall and an
outer wall, and the flapper seals are mounted on the outer wall of
the tube so that they extend outward from the tube. In still
another alternative embodiment, the middle section and the upper
section can form an integral tube that is threadably connected to
the lower section.
A preferred method for auto-cycling plunger lift takes place in a
gas or oil well having a lubricator positioned at the top of the
production string tubing and a bottom-hole bumper spring positioned
at the bottom of the production string. The lubricator preferably
comprises an arrival spring and a catcher. The preferred method of
this invention comprises the following steps: stopping production
flow; placing auto-cycling plunger with a detachable valve member
in the lubricator so that they are held by the catcher, the
auto-cycling plunger comprising a retrieval end and flapper sealing
rings; starting production flow so that gas well is pressurized;
releasing the catcher thereby allowing the detachable valve member
and auto-cycling plunger to fall independently through the
production string tubing until liquid in the bottom of the well
collects at top of plunger; striking bottom-hole bumper spring with
detachable valve member; striking bottom-hole bumper spring with
plunger so that the retrieval end of the plunger captures the
detachable valve member causing a valve seal within the plunger as
formation gas pressure pushes against the detachable valve
member;
Preferably, a seal is effected between flapper sealing rings and
the walls of the production string tubing; allowing formation gas
pressure to push plunger with captured detachable valve member
upward thereby pushing liquid above plunger towards top of
production string tubing; drawing off liquid and piping out gas as
plunger reenters lubricator thereby reducing pressure below plunger
allowing detachable valve member and plunger to fall back down
production string tubing repeating steps e) through j) without
shutting in well.
In the preferred method, the retrieval end of the lower section
comprises an inner wall and an outer wall, the inner wall defining
at least one groove for receiving an 0-ring, the 0-ring sized so
that it fits snugly about the detachable valve member when the
detachable valve member is engaged within the retrieval end of the
plunger. The inner wall of the retrieval end can form a sealing
groove and an 0-ring is fitted within the sealing groove for
sealing the lower section when the detachable valve is engaged
within the retrieval end.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 illustrates one embodiment of the auto-cycling plunger.
FIG. 2 is a cross-sectional view of FIG. 1
FIG. 3 is an exploded view of the flexible sealing ring during
downward travel.
FIG. 4 is an exploded view of the disc seals during upward
travel.
FIG. 5 is a view of the bullet shuttle.
FIG. 6 is a cross-sectional view of a one piece auto-cycling
plunger
FIG. 7 is a schematic of one method of auto-cycling plunger lift
illustrating the well and lubricator system.
DETAILED DESCRIPTION OF THE INVENTION
The auto-cycling plunger 10 of this invention lifts out condensate
and fluid that accumulate and retard production in oil and gas
wells. The improved sealing of the auto-cycling plunger allows a
minimum amount of gas to lift the plunger and the column of liquid
(oil, water, condensate etc.) above the plunger up the production
tubing and out of the well. During the method of this invention,
the auto-cycling plunger free falls down the production tubing
string until it hits the bottom-hole spring and collects the liquid
above it. It then moves up the production tubing as gas within the
well accumulates below it and creates an upward pressure. Because
of its unique tube and detachable valve arrangement, the
auto-cycling plunger repeats it's movement up and down the well
without requiring shut-in of well thereby continuously removing
liquids without stopping production.
The apparatus and method of this invention can be adapted to either
an oil or a gas well. In the detailed description of this
invention, the discussion is limited to a gas well, but the
invention is applicable to oil or gas production wells. Referring
to FIGS. 1 and 2, the preferred autocycling plunger comprises a
tube 15, a detachable valve 80 that can sit within a lower section
60 of the tube 15 and flapper sealing rings 40 that are mounted
along the tube 15. The tube 15 defines a continuous chamber 16 that
allows gas to freely move through it. The tube 15 comprises an
upper section 20, a middle section 30, and the lower section 60. In
one embodiment, the upper section 20, middle section 30 and lower
section 60 comprise three separate pieces that are threadedly
connected to each other. The middle section 30 comprises a central
mandrel 32 that is threaded on either end 26, 38 for engaging with
the upper and lower sections 20, 60. Flapper sealing rings 40 are
mounted onto the central mandrel 32 to create a seal between the
plunger and the production tubing 55 or well casing. One or more
spacers 35 surround the central mandrel 32 to separate the sealing
rings 40 and hold the sealing rings 40 firmly in place when the
upper and lower sections 20, 60 are tightly threaded onto the
central mandrel 32.
In one preferred embodiment, the upper section 20 is threaded on
one end for connecting to the middle section, 30. Alternatively, as
illustrated in FIG. 6, the upper section and middle section 30 are
integral and form one continuous tube. Alternatively, the upper
section 20 middle section 30 and lower section 60 can comprise one
integral unit with a continuous chamber 16. Preferably, the upper
section of the plunger 10 in any of the described embodiments can
comprise one or more internal grooves 22 opposite the threaded end,
the internal grooves 22 are adapted for engaging with a retrieval
tool for retrieval of the plunger from the well, if necessary. The
configuration of internal grooves 22 is known in the art as an
internal fishneck.
As illustrated in FIGS. 1 and 2, the middle section 30 preferably
comprises a hollow central mandrel 32, flapper sealing rings 40 and
removable spacers 35 for securing the sealing rings 40. The central
mandrel 32 defines a hollow central chamber 16 that is unobstructed
so that the auto-cycling plunger 10 can free fall down the
production tubing during the downward cycle with the least amount
of friction within the chamber. Preferably, the ratio of the
diameter of the central chamber 16 to the production tubing is
approximately 0.625 or greater to achieve the free fall effect.
The flapper sealing rings comprise an inner ring 43 and an outer,
flimsy sealing membrane 45. Preferably the inner ring 43 is
comprised of rigid material such as metal, hard elastomeric or
plastic to give form and shape to the sealing ring 40. The outer
sealing membrane 45 is flexible in that its shape can be somewhat
distorted then returned to its natural shape without damage to the
membrane 45. The ability to return to shape is common to
elastomeric products. The flexible sealing membrane 45 is fixably
attached in a vulcanizing process to the metallic inner ring 43.
The outer edge of the sealing membrane makes sealing contact with
the production tubing wall 55 as seen in FIG. 4. When used with the
method of this invention, the sealing rings 40 form a barrier
membrane separating the gas volume below the plunger 10 from the
fluid load above the plunger 10.
It is understood that the flexible sealing membrane 45 can also be
affixed to a one-piece molded unit as shown in FIG. 6.
One preferred embodiment of the sealing membrane 45 is flimsy in
that it has the ability to readily abandon its natural shape and to
bend in the presence of a limited applied force. The membrane 45
offers very little resistance to a shape change. The sealing
membrane 45 is preferably sufficiently thin for flexibility and to
counteract the effects of gas entrainment. The preferred flapper
sealing membrane 45 has a width to thickness ratio within a range
of from about 0.10 to about 0.20. Another important feature of the
flimsy sealing ring is that it does not cause excessive friction at
the tubing interface during its free fall down the tubing. Friction
at the interface is greater on the up-travel because it is
pressure-induced. However, the pressure, typically at 3 PSI, over a
contact area of less than 0.2 sq. inches, does not create excessive
friction. Preferably the sealing membrane 45 is comprised of an
elastomeric material, either rubber, or more preferred, urethane
type material.
Referring to FIGS. 3 and 4, the seal is preferably oversized in
relation to the production tubing to insure a positive seal. FIG. 3
illustrates the shape of the sealing membrane 45 during the
downward fall as it curls against the wall of the production tubing
55. The oversizing causes the seal to partially curl. The curl is a
major attribute of this feature of the invention. The pressure on
the inside of the curl of the sealing membrane 45 pushes equally
against all of the membrane 45 including the very edge portion
which is in contact with the production tubing wall 55. This
contact and the pressure behind it makes the seal possible. FIG. 4
illustrates the shape of the sealing member 45 during the upward
travel of the auto-cycling plunger 10 as the gas pressure under the
sealing member 45 causes a domed shape.
The outer diameter of the sealing membrane 45 is from about 3% to
about 6%, preferably 5%, larger than the inner diameter of the
production string tubing. This dimension produces an interference
fit between the sealing member 45 and the inner tubing wall 55. The
interference fit causes the membrane to roll-form into a
constricted shape and diameter that exerts a sealing contact with
the inner production tubing wall 55.
The preferred shape of the sealing membrane 45 is planer in
construction with a width to thickness ratio that allows the
membrane to form, when in use, an optimized shape. The shape
assumed by the elastomeric sealing membrane 45 balances the
pressure differential across the plunger with the drag created by
the seal contact area. The shape assumed by the sealing membrane 45
balances the differential by allowing and encouraging the plunger
10 to move in that direction that reduces the differential. The
drag created by the sealing membrane 45 as it rubs the production
tubing wall 55 is a function of the coefficient of friction of the
elastomer against steel. The sealing membrane 45 is preferably
larger than the tubing 55 to encourage definite contact with the
tubing wall. The size and interference fit of the seal produces a
shape of seal 45 that encourages lift over drag.
The number of flexible sealing rings used is a variable dependent
on the well application. Some wells have multiple weight tubing,
i.e. varying dimensions. The number of and the thickness ratio for
the seals will vary accordingly and can be easily determine by
those in the art. The width to thickness ratio of the membrane 45
is sufficient to hold the differential pressure and thin enough to
permit the sealing membrane 45 to change shape and roll into a new
shape during reciprocation of travel. In a preferred embodiment,
one or more spacers 35 are slideably positioned over the central
mandrel 32 to separate the flexible sealing rings 40. The outside
diameter of the upper section 20, lower section 60 and the spacers
35 is approximately 2% to 8% smaller than the inner diameter of the
production tubing. Preferably, the outside diameter of the upper
section 20, lower section 60 and the spacers 35 is approximately 5%
smaller than the inner diameter of the production tubing. This
diameter sizing provides clearance for free movement of the
auto-cycling plunger 10 inside the tubing. This novel plunger is
capable of operating in a tubing string 55 or a casing string, i.e.
a well without production tubing.
Preferably, the lower section 60 defines a hollow chamber
continuous with the hollow chamber of the upper section 20 and
middle section 30. The lower section 60 is threaded onto the
central mandrel 32 thereby holding the spacers 35 and sealing rings
40 in place. In one preferred embodiment, the lower section 60
forms a retrieval end 63. The retrieval end 63 is designed for
retrieval of the detachable valve 80 at the bottom of the
production string 55. The internal walls of the retrieval end 63
are grooved for O-rings 64, 67. One groove 62 and O-Ring 64 are for
sealing the continuous chamber 16 when the tube 15 is engaged with
the detachable valve 80. The second groove 66 and second O-Ring 67
are shaped to receive and engage the detachable valve 80 of the
plunger 10 within the retrieval end 63 of the tubing 15. The
retrieval end is preferably angular-shaped to align and receive the
detachable valve 80. In one aspect, the retrieval end 63 has an
inner diameter, not including O-rings 64, 67 within a range of from
about 1/4 mm to about 3 mm larger than the detachable valve 80.
Preferably, the very most lower edge 68 of the lower section 60 is
sharply angled to form a scraper. Paraffin often collects along the
inner wall of the production tubing 55 and the knife edged scraper
68 can function to remove paraffin during the free fall of the
auto-cycling plunger 10 down the production tubing.
FIGS. 2 and 5 illustrate the detachable valve 80 of this invention
when engaged with the tube 15. As the auto-cycling plunger 10
begins its free fall down the production string tubing 55, the
detachable valve 80 separates from the tube 15 because of reduced
gas pressure. This will be discussed in more detail during the
description of the method of this invention. In a preferred
embodiment, the detachable valve 80 is a sphere sized to be
received within the retrieval end 63 as illustrated in FIG. 2. This
sphere-shaped valve can be referred to as a ball shuttle valve 80.
Alternatively, the detachable valve 82 can be elongated with a
rounded end as illustrated in FIG. 5, this embodiment is referred
to as a bullet shuttle valve 82. The rounded shape of either
embodiment of the detachable valve 80, 82 facilitates central
alignment within the retrieval end 63 when the valve 80, 82 engages
with the tubing 15. One preferred detachable valve 80 is made from
metallic or elastomeric material or a combination thereof. The
bullet shuttle valve 82 can also be made from metallic or
elastomeric material or a combination thereof. Either embodiment
80, 82 can vary in density to accommodate well conditions.
The detachable valve 80, 82 has a smaller surface area to weight
ratio than the main body or tube 15 of the plunger 10. In one
preferred embodiment, the detachable valve 80, 82 has a ratio of
16.5, whereas the main body has a surface area to weight ratio of
28. This ratio means the main body produces more drag relative to
the traveling valve 80, 82. This extra drag, plus the minimal drag
at the seal interface, causes the main body to fall at a slower
rate than the detachable valve 80,82. The detachable valve 80, 82
can also be referred to as a traveling valve because it detaches
from the tubing 15 and free falls down the production string 55
apart from the tubing 15.
Referring to FIG. 2, the lower section further comprises a choke 51
positioned in the chamber 16 above the first groove 62. The choke
51 can be a washer that is fixed into the chamber 16 as a limited
restriction. The purpose is to slow down the fall rate of the tube
15. To slow down the fall rate of the traveling valve, a lighter
density design is used such as the bullet shuttle. The use and
design of chokes are well know in the art.
FIG. 7 is a schematic illustrating the method of auto-cycling
plunger lift. The method for auto-cycling plunger lift is practiced
in a gas well having a lubricator 50 positioned at the top of the
production string tubing 55 and a bottom-hole bumper spring 56
positioned at the bottom of the production string 55, the
lubricator 50 comprises an arrival spring 51, which cushions the
arrival of the plunger 10 within the lubricator 50, and a catcher
52. The lubricator 50 is a special piping arrangement installed for
plunger lift. It is positioned on top of the well to capture the
auto-cycling plunger 10. The lubricator 50 also has an outlet pipe
53 for piping out the production gas. The flow of gas production is
stopped when the master valve 54 is closed. The top of the
lubricator 50 is then opened and the auto-cycling plunger 10 with
its detachable valve member 80 is placed within and held in place
by the catcher 52. The production flow is restarted so that the gas
well is pressurized and the catcher released thereby allowing the
plunger 10 to begin free fall down the production string tubing 55.
Because the gas pressure is not sufficient to hold the detachable
valve 80 within the retrieval end 63 of the auto-cycling plunger
10, the detachable valve 80 separates from the auto-cycling plunger
10 and falls independently through the production string tubing 55.
The tube 15 of the auto-cycling plunger 10 is a hollow cylinder and
allows the gas and liquid in the production string 55 to pass
through its central chamber 16 until liquid in the bottom of the
well collects at the top of plunger 10. The detachable valve 80
strikes the bottom-hole bumper spring 56 first and the tube 15
follows. The tube 15 strikes the bottom-hole bumper spring 56. Upon
striking the bottom-hole bumper spring 56, the retrieval end 63 of
the plunger 10 engages with the detachable valve member 80 so that
the valve 80 effects a snug valve seal within the auto-cycling
plunger 10 as formation gas pressure pushes against the detachable
valve member 80. Preferably, the internal walls of the retrieval
end 63 are grooved for O-rings 64, 67 as depicted in FIG. 2. One
groove 62 and O-Ring 64 are for sealing the continuous chamber 16
when the tube 15 is engaged with the detachable valve 80. The
second groove 66 and second O-Ring 67 are shaped to receive and
engage the detachable valve 80 of the plunger 10 within the
retrieval end 63 of the tubing 15.
In a preferred method of this invention, a seal is also effected
between the flapper sealing rings 40 and the walls of the
production string tubing 55. Because the flow outlet at the surface
remains open during this method, the formation gas inflows the
bottom of the production string tubing 55. Formation gas pressure
pushes the auto-cycling plunger 10 with its captured detachable
valve member 80 upward thereby pushing liquid above plunger 10
towards the top of production string tubing.
Preferably, the liquid is drawn off and the gas piped out as the
plunger 10 reenters the lubricator 50 thereby reducing pressure
below plunger 10. When the pressure is reduced below the plunger
10, the detachable valve member 80 falls away from the plunger 10
breaking the seal and thereby allowing the plunger to fall back
down the production string tubing 55. These steps of the method of
auto-cycling plunger lift are repeated automatically and without
shutting in well or leasing production.
EXAMPLE
A test stand of 2" I.D. clear tubing was used to view the pad
plunger and the global change to auto-cycling plunger in action.
The lower portion of the tubing was filled with water. The pad
plunger was dropped into the tubing from a height of 20'. The pad
plunger fell through the (atmospheric) upper portion of the tubing
at a rate of 10'/second. The fall rate through the water was
1'/second. Shop air was applied to the bottom of the test-stand
tubing to simulate a flowing well. The pad plunger rose with the
water and bubbles until the density of the water would no longer
support the weight of the plunger and it fell back to the bottom.
The pad plunger stayed on bottom even though the water and air
boiled around and past it.
The shop air supply was rated at 13 MCFD at 40 PSI continuous. The
instantaneous rate through the supply line is 39 MCFD @ 110 PSI. A
higher flow rate from the compressor would have uplifted the pad
plunger to the surface. This test created a baseline for
measurements of efficiency of the auto-cycling plunger of this
invention. The test stand included a means for returning water to
the bottom of the tubing. A sufficiency of water in the system
insured a ready supply at the bottom of the tubing to match the
conditions of a gas well. Likewise, the air from the compressor was
vented at the surface.
For the second phase of testing, the shuttle bullet and plunger
were dropped into the clear tubing. The fall rate through the fluid
was 3.70 feet/second for the plunger. When shop air was applied to
the bottom of the tubing, the plunger and shuttle rose as a unit to
the top of the tubing. As the plunger rose swiftly to the top, it
pushed 100% of the water above it to the surface. The tubing below
the rising plunger was wiped clear of liquids just as a windshield
wiper cleans an automotive windshield. At the top of the tubing, a
tee had been installed to divert the fluids in a circuitous manner
to the bottom of the clear tubing. When the auto-cycling plunger
passed above the tee, the shuttle portion of the plunger lost its
holding force with the tube due to the loss of the differential
pressure across the plunger. The shuttle fell, followed momentarily
by the auto cycling plunger.
The water reservoir had let more water into the bottom of the
tubing. The shuttle and plunger each fell through this water before
rejoining at the bottom of the tubing. The air input was still
active. The moment the shuttle and plunger rejoined, closing the
by-pass, the plunger moved again to the surface. This cycle of rise
and fall and water movement to the surface was repeatable and
continuous. If the air input was closed during the rising phase of
the cycle, the plunger and shuttle would stall in the tubing. To
stall in the tubing without falling backwards is a desirable
feature.
The foregoing description is illustrative and explanatory of
preferred embodiments of the invention, and variations in the size,
shape, materials and other details will become apparent to those
skilled in the art. It is intended that all such variations and
modifications which fall within the scope or spirit of the appended
claims be embraced thereby.
* * * * *